David Hartley vanished on Sept. 30 while jet skiing with his wife on Falcon Lake.

Tiffany Hartley said they were chased across the lake by men in speedboats as they returned from a trip to photograph a Mexican church. Neither David Hartley's body nor the Jet Ski has been recovered.

Hartley, of McAllen, Texas, is believed to have been shot by Zetas cartel enforcers because he was mistaken for an operative of the rival Gulf cartel, according to an independent intelligence report.

"The truck Hartley and his wife used to put their Jet Skis in the water at the lake had Tamaulipas state plates, and the Hartleys drove the Jet Skis to the Old Guerrero area of the lake, a known battleground in the ongoing war the Los Zetas and Gulf cartels," according to STRATFOR, a Texas-based think tank on intelligence and international issues.

"Given the couple’s license plate and method and direction of travel, it is possible that Zetas scouts identified them as a Gulf cartel surveillance team," STRATFOR said in its report.

"A damage control campaign is currently under way, led by Los Zetas No. 2, Miguel 'Z-40' Trevino Morales, to identify and eliminate those who engaged the Hartleys without proper authorization," according to the report.

It said Hartley's body had been destroyed as part of that effort.

The war between the Zetas and Gulf cartels erupted earlier this year over a fatal shooting and has spread through the Tamaulipas border region, Gonzalez said.

On Tuesday, the beheading of Rolando Armando Flores Villegas, the lead Mexican investigator in the Hartley case, was a chilling reminder of the cartel's brutal intimidation tactics.

Texas officials have long warned boaters and fisherman that pirates frequent the Mexican side of the lake, a 30-mile by 3-mile dammed section of the Rio Grande, Gonzalez said.

"The cartels do not normally target American citizens not involved in the narcotics trade, but cases of mistaken identity have occurred in the past," STRATFOR said.

Nonetheless, the lake can be treacherous, Gonzalez said.

"Anyone going into the area is going to get stopped and checked by the cartels," he said. "They have machine guns. They will pull you aside, grab you, put you on their boat face down, and with their knees into your back and a machine gun into your head, they will ask you who you are."

Gonzalez said the Hartleys tried to flee after they were stopped "and the shooting started. One unlucky shot hit in the man in the head."